Frequently, powder-actuated tools are employed to drive steel pins or fasteners through workpieces into steel, concrete, or masonry substrates. A powder-actuated tool employs a powder charge, which undergoes explosive combustion.
High velocity tools, those without pistons, are no longer produced in the industry. Current low velocity, powder-actuated tools drive the steel pins or fasteners by means of a piston disposed between the charge and the steel pin. These current low velocity tools result in lower velocity of the steel pin and thus lower energy imparted to the pin. Without proper design and manufacture of the steel pin or fastener, these tools may not have sufficient energy to drive a fastener into a steel substrate deeply enough to provide adequate or consistent holding values to satisfy the needs of a specific application. Without a properly designed pin, some would-be powder-actuated tool users may opt for other methods of holding articles to steel or concrete, such as inserting a fastener into a drilled hole.
Typically, such a pin is manufactured by drawing a steel wire to a desired diameter, cutting a length of the drawn wire while deforming one end of the length to form a head, and deforming the other end thereof to form a point. Typically, the steel pin is next heat-treated, as by austempering which produces a ductile core in combination with surface decarburization, and then plated with zinc, as by electrogalvanizing. Various additional coatings may be also applied to further improve corrosion resistance.
Commonly, the point is formed either by swaging the wire end or by pinch pointing, which refers to forging the wire end between two matched dies. Each point-forming process, as practiced heretofore, has its own shortcomings.
Swaging is a slower process. Swaging tends to form a protuberance at the point. The protuberance tends to bend over, to deflect the steel pin, and to increase resistance to penetration, particularly as the steel pin is driven initially against a steel surface, whereby it may be unduly difficult to maintain perpendicularity of the steel pin relative to the steel surface.
Pinch pointing is a faster process. Pinch pointing tends to form a cleft where the matched dies come together at the tip. Because of its striking appearance under high magnification (e.g. 60.times. magnification) the cleft that is formed is known as a "fish mouth" to persons involved with the manufacture of steel pins.
In addition to resulting in a tip having either a protuberance or a "fish mouth", both swaging and pinch pointing processes make it difficult to produce a smooth transition, which is required, where the pointed end of the steel pin meets the cylindrical shank of the steel pin.
Generally, a "fish mouth" cleft does not seem to interfere unduly with driving of a steel pin having such a cleft into a concrete or masonry substrate via a powder-actuated tool, even if the steel pin must be initially driven through a thin-walled steel workpiece. However, such a cleft tends to increase resistance to penetration to such a high level that a steel pin having such a cleft cannot be effectively driven via a low velocity powder-actuated tool so as to penetrate deeply into a steel substrate. Although a larger powder charge aids penetration of a steel pin into a steel substrate, such penetration is not always successful even if such a charge is employed.
When a low velocity tool is employed, penetration of a steel pin having such a cleft into a steel substrate tends to be arrested before all energy from the powder charge that has been employed has been spent, whereupon the steel pin may break along its shank. It may be similarly difficult to drive a steel pin having such a cleft through a thick-walled steel workpiece via a powder-actuated tool.
Other alternative mechanical processes for forming a point on such a pin include turn pointing and roll pointing. These processes leave undesirble flaws, such as grooves in the point or a sharp transition between the point and the shank. It is believed that, in every pin such known to the prior art, there is some section that has a gross surface imperfection deviating from the desired ogive shape.
Heretofore, it has been known to remove slight imperfections and small burrs by tumbling steel pins upon themselves, with or without media. As practiced heretofore, tumbling only is not entirely satisfactory, as tumbling tends to distort the clefts or protuberances on the points of the tumbled pins. Because of the distorted points, it can be more difficult to maintain perpendicularity of such pins relative to steel substrates, and resistance to penetration of such pins into steel substrates tends to be also increased.
The purpose of tumbling practiced heretofore was to remove flash or upstanding thin-walled protuberances on the steel pin, commonly known as deburring. The purpose was not to remove steel from most of the surface of the tip of the pin.